Double discharge system and device thereof

ABSTRACT

A system for imparting charge to a chargeable member wherein corona discharge electrodes each having an associated auxiliary electrode are disposed on alternate sides of the member. A voltage of first polarity is applied exclusively to all corona discharge electrodes on one member side and to all auxiliary electrodes on the other member side. A voltage of opposite polarity is applied to all other corona discharge electrodes and auxiliary electrodes. The system is further disclosed in preferred charging apparatus having said electrodes insulatively supported therein and incorporating a passage for transport of said chargeable member through the apparatus. Circuit means is shown for providing dissimilar potentials for the auxiliary electrodes and the corona discharge electrodes.

United States Patent Tanaka et al.

[4 1 Mar. 21, 1972 DOUBLE DISCHARGE SYSTEM AND DEVICE THEREOF Hiroshi mm; Glichi Marushiml; Shinkichi Takahashl, all of Tokyo, Japan Assignee: Canon Kabushiki Kaisha, Tokyo, Japan Filed: Oct. 27, 1967 Appl. No.: 678,614

lnventors:

u.s. Cl. ..2s0/49.s zc, 3 17/ 262 A Int. Cl. .003; 15/02 Field of Search ..2s0/49.s; 317/4, 262, 262 A; 95/10 References Cited UNITED STATES PATENTS 10/1958 Rosenthal ..250/49.5

1/1959 Haackem, 5/1959 Gundlach ....250/49.5 1/1960 Giaimo, Jr. ..250/49.5

3,164,074 l/l965 Francis et al ..250/49.5 X 3,277,298 10/1966 Tiger et al..... ..250/49.5

3,374,348 3/1968 Ostensen ..250/49.5

Primary Examiner-William F. Lindquist Attorney-Watson, Leavenworth & Kelton [5 7] ABSTRACT A system for imparting charge to a chargeable member wherein corona discharge electrodes each having an associated auxiliary electrode are disposed on alternate sides of v the member. A voltage of first polarity is applied exclusively to all corona discharge electrodes on one member side and to all auxiliary electrodes on the other member side. A voltage of opposite polarity is applied to all other corona discharge elec- I trodes and auxiliary electrodes. The system is further disclosed in preferred charging apparatus having said electrodes insulativelysupported therein and incorporating a passage for transport ot 'said chargeable member through the apparatus. Circuit means is shown for providing dissimilar potentials for the auxiliary electrodes and the corona discharge electrodes.

13 Claims, 5 Drawing Figures PATENTEDmzi m2 ml' kk This invention relates to a charging system and device for imparting an electrostatic charge to a photosensitive sheet member in electrophotography, particularly in an electrofax system.

In the prior art electrophotographic process of the electrofax system, means have been provided for imparting an electrostatic charge to a photosensitive member comprising a coating of photoconductive material on a support member. In

this prior art system, the surface of the support member of the photosensitive member is placed in contact with a grounded conductive base plate and an electrostatic charge is imparted to the thin photoconductive layer by corona discharge. In accordance with other prior art such as disclosed in U.S. Pat. No. 2,922,883 issued to E. C. Giaimo Jr. on Jan. 26, 1960, two corona discharge electrodes are placed opposite each other, conductive shield members, each surrounding the associated corona discharge electrode and electrically isolated therefrom are grounded, and high voltages of respectively opposite polarities are applied to the corona discharge electrodes to produce double corona discharge for bombarding one surface of a photosensitive member inserted therebetween with negative ions and the opposite surface of the member with positive ions, respectively. In the first-discussed prior art system it is necessary that the support member of the photosensitive layer have relatively high conductivity during the initial stage of charging the photosensitive member, and furthermore, nonuniformity of charge is apt to be produced as the degree of contact between the conductive base plate and the support member of the photosensitive layer varies. In the seconddiscussed prior art system, it is unnecessary that the support member be conductive during charging and it is also unnecessary that the base plate be conductive. However, a much higher voltage supply must be provided than in the firstdiscussed system which goes against the desired minimization of high voltage requirements. There results a bulky and expensive high voltage supply which is difficult to maintain.

An object of the invention is to provide an improved charging system and device using double corona discharge.

A further object of the invention is to provide an improved charging system and device using double corona discharge provided with corona discharge electrodes and auxiliary electrodes wherein it is unnecessary to use grounded shield plates.

An additional object of the invention is to provide an improved charging system and device using double corona discharge in which voltages applied to corona discharge electrodes are relatively low.

A still further object of the invention is to provide an improved charging system and device using double corona discharge wherein charge may be controlled by adjusting voltage applied respectively to the corona discharge electrode and the auxiliary electrode.

The charging device of this invention comprises corona discharging electrodes provided respectively adjacent opposite surfaces of a photosensitive member comprised of a thin photoconductive layer on a support member, and auxiliary electrodes associated with each corona discharging electrode are electrically insulated therefrom. High voltages of respectively opposite polarity are applied to the corona discharging electrodes on alternate sides of the member. High voltage of opposite polarity to that applied to each corona discharging electrode is applied to the auxiliary electrode associated therewith. The voltage of the corona discharging electrodes can be kept higher than or equal to the voltages of the auxiliary electrodes. The charging device thus imparts negative corona discharge to one of the surfaces of the photosensitive member, and at the same time imparts positive corona discharge to the other surface to electrostatically charge the photoconductive layer.

According to the present invention, one of the corona discharge devices produces a negative corona bombarding of one surface of the photosensitive member with negative ions, while the other corona discharge device produces a positive corona bombarding of the opposite surface of the member with positive ions. With this arrangement, the opposite surfaces of the photosensitive member are oppositely charged so that, effectively, a zero potential plane is formed in the interior of the photosensitive member without using a conductive base plate, and therefore, there is no fear of non-uniformity of charge heretofore caused by changes in the contact between the surface of the photosensitive member and the conductive base plate. In accordance with the invention, the support member of the photosensitive layer may be insulating or conductive which is advantageous in that electrostatic charges can be imparted to the member under relatively low humidity. Furthermore, it is important to note that according to the present invention, since voltage of a polarity opposite to that applied to each corona discharge electrode is applied to the auxiliary electrode associated therewith, the voltage applied to the corona discharge electrode for generating corona is significantly lowered in comparison with the prior art systems, which results in a desirably compact and less expensive electrophotographic device.

The present invention will be more apparent from the following detailed description of the embodiment thereof shown in the drawings in which:

FIG. 1 is a perspective view of an illustrative embodiment of the present invention;

FIG. 2 is a lateral cross-sectional view of the embodiment of FIG. 1;

FIG. 3 is a vertical cross-sectional view of the embodiment of FIG. 1;

FIG. 4 is a partial perspective longitudinal view of the embodiment of FIG. 1 in which the upper portion of the case is removed; and

FIG. 5 shows a corona discharge circuit used for the embodiment of the invention as shown in FIG. 1.

Referring to FIG. 1 cases 1, l constitute a housing for the illustrated charging device and are composed of insulating materials such as bak'elite, and the cases can be separated on line A. Slot 2 is a lateral slot for receiving a photosensitive member. Leads 3 and 3 and 4 and 4 connect corona discharge electrodes 5 and 5' and the auxiliary electrodes 6 and 6' to high voltage electric source 7, and are connected to the terminals of the respective electrodes on the sides of the cases.

FIG. 2 through FIG. 4 show the details of the internal arrangement of the device of FIG. 1, in which 5 and 5' are corona discharge electrodes each comprised of three tungsten wires stretched within the cases I, 1' along the lengthwise direction of a photosensitive member passing through lateral slot 2. Each of both ends of the wires are stretched by springs 8, 8' toward electrode supporting conductive plates 10 and 10 which are fixed by screws 9 and 9 onto cases 1, l. Electrode supporting plates 10 and 10' have terminals 11 and 11' connected respectively to conductors 3 and 3'. Auxiliary electrodes 6 and 6', shaped almost semicircularly and composed of aluminum or copper, are fixed to the case by screws 12 and 12', respectively, so as to surround the associated corona discharge electrodes 5 and 5. Auxiliary electrodes 6 and 6' extend parallel to the electrodes 5 and 5, respectively, and are electrically isolated therefrom. At each end of the auxiliary electrodes 6, 6' is formed a terminal 13, 13, connected respectively to conductors 4 and 4.

It is preferable to make the space between the corona discharge electrodes 5 and 5 equal to or a little less than the spaces between the corona discharge electrodes 5 and 5' and the auxiliary electrodes 6 and 6', for effectively utilizing the corona discharge.

Referring to FIG. 5 in using the charging device having the above-described structure, corona discharge electrode 5 is connected to the positive high voltage terminal of high voltage electric source 7 by conductor 3, and electrode 5' is connected to the negative high voltage terminal of high voltage electric source 7 by conductor 3'. Auxiliary electrode 6 is connected to the negative high voltage terminal of high voltage electric source 7 by conductor 4 through resistor 14, and electrode 5' is connected to the positive high voltage terminal of high voltage electric source 7 by conductor 4' through resistor 14. Resistors l4 and 14 are for adjusting the voltage applied to the respective auxiliary electrodes 6 and 6, and may be fixed or variable resistors. They are adjustably set independently or interlocked to each other, if necessary. Element 15 is a photosensitive member having a thin photoconductive layer 17 on a support member 16.

In such a structure as above, the thickness of the tungsten wire of corona discharge electrodes 5 and 5' is selected to be from 0.05 to 0.1 mm., and the space between electrodes 5 and 5 is determined to be from 10 to 20 mm. A positive voltage from three to four kv. is applied to corona discharge electrode 5, and a negative voltage from three to four kv. is applied to electrode 5' by means of high voltage electric source 7. A

negative voltage from 1.5 to 2 kv. is applied to auxiliary electrode 6 by adjusting resistor 14, and a positive voltage from 1.5 to 2 kv. is applied to electrode 6' by adjusting resistor 14' by means of high voltage electric source 7. In this state, photosensitive layer 17 of photosensitive member 15 is directed towards electrode 5' and member 15 is inserted into slot 2 of cases 1, l, and photosensitive member 15 is advanced to a position intermediate corona discharging electrodes 5 and 5 by appropriate means not shown in the drawing. In this position, photosensitive layer 17 of the photosensitive member is charged in the negative by receiving the negative ions because of the negative corona discharge of electrode 5', and simultaneously support member 16 receives the positive ions caused by the positive corona discharge of electrode 5, and is charged in the positive.

Thus, both surfaces of photosensitive member 15 are charged simultaneously by positive and negative double corona discharge, and therefore both surfaces of the photosensitive member are charged in opposite polarity, and a zero potential interface is effectively formed inside the photosensitive member. In carrying out the charging operation it is not necessary to use a conductive base plate. Where a conductive base plate is used, non-uniformity of electrostatic charge, attributable to the change in contact between the conductive base plate and the surface of the photosensitive member, is not brought about, and the whole surface of the photosensitive layer can be uniformly charged, and advantageous electrostatic charges attained by double corona discharge are provided.

Further, in this invention, almost semi-circular auxiliary electrodes 6 and 6 are provided around the corona discharge electrodes 5 and 5' and are electrically insulated from said corona discharging electrodes, and a voltage of opposite polarity, equal to or a little less than the voltage applied to the corona discharging electrodes, is positively applied to the auxiliary electrodes associated therewith, and therefore there is such an effect that the distribution of the electric field becomes remarkably uniform, and the generation of corona becomes easy, and the corona generating voltage becomes sufficicntly low.

In other words, when this invention is compared with the prior art systems with other conditions almost equal, a voltage of from five to six kv. is required in the prior art systems to be applied to the corona discharge electrodes when the interval between the photosensitive member and the electrodes is selected to be from 10 mm. to 20 mm. and the tungsten wire thickness is from 0.05 mm. to 0.1 mm. But according to this invention, a voltage of from three to four kv. is applied to the corona discharge electrodes and a voltage of from one to two kv. is applied to the auxiliary electrodes, and sufficient corona can be generated. Therefore, the electric source voltage is reduced by about percent when compared with the prior art systems, and the voltage applied to the auxiliary electrodes can be supplied by appropriate voltage drop from the same electric source as used for the corona discharge electrodes, and therefore the high voltage electric source can be minimized and economized, which is especially desirable in electrophotographic devices.

When the voltage applied to the electrodes is adjusted to be the same as the voltage of the conventional devices, and when the same corona discharges are generated, the diameter of the wire of the corona discharge electrodes can be made thicker, and the attachment of the wires to the charging device becomes easy, and the charging device becomes stronger, and the manufacturing and the maintenance of the charging device is remarkably simplified.

Moreover, according to this invention, the voltage applied to the auxiliary electrodes can be very easily adjusted by change of the resistor connected to the same circuit, and therefore the amount of electrostatic charge applied to the photosensitive layer can be optionally selected by adjusting the relative voltage of the auxiliary electrodes as against corona discharging electrode voltage.

Thus, this invention has such an effect that the adjustment can be easily done even when half tone is reproduced, or when the thickness of photosensitive member, or the resistor or the like is greatly changed.

The form of the auxiliary electrode is not restricted to the form given in the illustrative embodiment, but the auxiliary electrodes of this invention can be obtained by parallel stretching of a plurality of conductors on the periphery almost coaxial with the corona discharge electrodes with appropriate spacing interval, or may be of semi-cylindrical form composed of mesh-like conductors, and these modifications are included in the'scope of the auxiliary electrodes of this invention as defined in the appended claims.

What is claimed is:

1. A system for charging a chargeable member comprising:

a. voltage supply means providing high voltages respectively positive and negative relative to ground potential;

b. first and second electrode assemblies respectively disposed on opposite sides of said member, each elec trode assembly including a corona discharge electrode disposed adjacent said member and a further electrode insulatively supported with respect to and partially encircling said corona discharge electrode and further spaced from said member; and

c. circuit means applying said high positive voltages to the corona discharge electrode of said first electrode assembly and the further electrode of said second electrode assembly and applying said high negative voltages to the corona discharge electrode of said second electrode assembly and the further electrode of said first electrode assembly.

2. The system claimed in claim 1 wherein said chargeable member is a photosensitive member.

3. The system claimed in claim 1 wherein each of said further electrodes is substantially semi-circular in cross section and definesan opening facing said chargeable member.

4. The system claimed in claim 1 wherein said voltage supply means provides first and second positive voltages and first and second negative voltages, said first voltages being of greater magnitude than said second voltages, said circuit means applying said first positive and said first negative voltages respectively to the corona discharge electrodes of said first and second electrode assemblies and applying said second positive and said second negative voltages respectively to the further electrodes of said second and first electrode assemblies.

5. The system claimed in claim 1 wherein said supply means provides voltages of equal magnitude and wherein said circuit means comprises conductive members of equal electrical resistivity connecting said electrodes and said voltage supply means.

6. The system claimed in claim 1 wherein said supply means provides voltages of equal magnitude and wherein said circuit means comprise first conductive members of equal electrical resistivity connecting said corona discharge electrodes and said voltage supply means and second conductive members of electrical resistivity greater than that of said first conductive members connecting said further electrodes and said voltage supply means. I

7. The system claimed in claim 6 wherein said second conductive members are of variable electrical resistivity.

8. The system claimed in claim 7 wherein said second. conductive members are interlocked in variable electrical resistivity.

9. The system claimed in claim 1 wherein the, corona discharge electrodes of said first and second electrode assemblies are spaced apart by a distance equal to or less than the distance between the corona discharge electrode and further electrode of each electrode assembly.

10. Apparatus for charging a photosensitive member comprising:

a. an insulative case having a transverse central opening therethrough for passage of said photosensitive member;

b. first and second corona discharge electrodes respectively secured insulatively in said case on opposite sides of said opening;

c. third and fourth electrodes respectively secured insulatively in said case on opposite sides of said opening and spaced a greater distance from said opening than said first and second electrodes, said first and third electrodes being positioned on the same side of said opening;

d. a high voltage power supply having first and second output terminals respectively providing a voltage positive relative to ground potential and a voltage negative relative to ground potential;

e. first circuit means connecting said first and fourth electrodes to said first power supply terminal;

f. second circuit means connecting said second and third electrodes to said second power supply terminal.

11. The apparatus claimed in claim 10 wherein said third and fourth electrodes are substantially semi-circular in cross section, partially encircle said first and second electrodes respectively and define openings facing said transverse central opening.

12. The apparatus claimed in claim 10 wherein said first circuit means includes a high resistance member connecting said fourth electrode and said first power supply terminal and wherein said second circuit means includes a high resistance member connecting said third electrode and said second power supply terminal.

13. The apparatus claimed in claim 12 wherein said high resistance members are variable resistances.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,651,323 Dated March 21, 1972 Inventor(s) Hiroshi Tanaka 6t 81.

It certified that error appears in the above-identified patent and that said Letters Patentare hereby corrected as shown belowr Title page, Item [54] "Double Discharge System and Device I I I Thereof" should read "Double Corona Discharge System and Device Thereof--.

' Signed and sealed this 17th day of April 1973 (SEAL) Attest: I r

EDW ARDM'TLETCHERJR. I ROBERT GOTTSCHALK .Attesting Officer 7 Commissioner of Patents O-1N0 0PM 3 59 USCOMM-DC 60376-P69 I U.S GOVERNMENT PRINTING OFFICE I 959 0*356-334 UNITED :STATES PATENT OFFICE CERTIFICATE OF CORREQTION Patent No. I 3,651,323 Dated March 21, 1972 Inventor(s) Hiroshi Tanaka etal.

It is eertified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Title page, Item [54] "Double Discharge 'System and Device I Thereof" should read --Double Corona Discharge System and Device Thereof--.

Signed and sealed this 17th day of" April 1973.

(SEAL) Attest: v

EDWARD IYLFLETCHERJR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM I O-1050 HO-E9 USCOMM-DC 50375-P69 U.S. GOVERNMENT PRINTING OFFICE: I969 O-36633d 

1. A system for charging a chargeable member comprising: a. voltage supply meanS providing high voltages respectively positive and negative relative to ground potential; b. first and second electrode assemblies respectively disposed on opposite sides of said member, each electrode assembly including a corona discharge electrode disposed adjacent said member and a further electrode insulatively supported with respect to and partially encircling said corona discharge electrode and further spaced from said member; and c. circuit means applying said high positive voltages to the corona discharge electrode of said first electrode assembly and the further electrode of said second electrode assembly and applying said high negative voltages to the corona discharge electrode of said second electrode assembly and the further electrode of said first electrode assembly.
 2. The system claimed in claim 1 wherein said chargeable member is a photosensitive member.
 3. The system claimed in claim 1 wherein each of said further electrodes is substantially semi-circular in cross section and defines an opening facing said chargeable member.
 4. The system claimed in claim 1 wherein said voltage supply means provides first and second positive voltages and first and second negative voltages, said first voltages being of greater magnitude than said second voltages, said circuit means applying said first positive and said first negative voltages respectively to the corona discharge electrodes of said first and second electrode assemblies and applying said second positive and said second negative voltages respectively to the further electrodes of said second and first electrode assemblies.
 5. The system claimed in claim 1 wherein said supply means provides voltages of equal magnitude and wherein said circuit means comprises conductive members of equal electrical resistivity connecting said electrodes and said voltage supply means.
 6. The system claimed in claim 1 wherein said supply means provides voltages of equal magnitude and wherein said circuit means comprise first conductive members of equal electrical resistivity connecting said corona discharge electrodes and said voltage supply means and second conductive members of electrical resistivity greater than that of said first conductive members connecting said further electrodes and said voltage supply means.
 7. The system claimed in claim 6 wherein said second conductive members are of variable electrical resistivity.
 8. The system claimed in claim 7 wherein said second conductive members are interlocked in variable electrical resistivity.
 9. The system claimed in claim 1 wherein the corona discharge electrodes of said first and second electrode assemblies are spaced apart by a distance equal to or less than the distance between the corona discharge electrode and further electrode of each electrode assembly.
 10. Apparatus for charging a photosensitive member comprising: a. an insulative case having a transverse central opening therethrough for passage of said photosensitive member; b. first and second corona discharge electrodes respectively secured insulatively in said case on opposite sides of said opening; c. third and fourth electrodes respectively secured insulatively in said case on opposite sides of said opening and spaced a greater distance from said opening than said first and second electrodes, said first and third electrodes being positioned on the same side of said opening; d. a high voltage power supply having first and second output terminals respectively providing a voltage positive relative to ground potential and a voltage negative relative to ground potential; e. first circuit means connecting said first and fourth electrodes to said first power supply terminal; f. second circuit means connecting said second and third electrodes to said second power supply terminal.
 11. The apparatus claimed in claim 10 wherein said third and fourth electrodes are substantially semi-circular in cross section, partially encircle said first and second electrodes respectively and define openings facing said transverse central opening.
 12. The apparatus claimed in claim 10 wherein said first circuit means includes a high resistance member connecting said fourth electrode and said first power supply terminal and wherein said second circuit means includes a high resistance member connecting said third electrode and said second power supply terminal.
 13. The apparatus claimed in claim 12 wherein said high resistance members are variable resistances. 